1. Field of the Invention
The invention relates to apparatus for drying material utilizing force circulated heated gas in contact with the material to be dried conveyed through a linear conduit section of the gas system and to a method of operating such an apparatus.
2. Description of the Prior Art
Single and multiple deck conveyor dryers for reducing the moisture content of various materials including rigid and semi-rigid material in sheet form, such as, green veneer, wet plasterboard, fiberboard , Perlite and bagasse mat, and the like, wherein the material being dried is conveyed through a stationary housing on one or a plurality of tiered conveyors while heated gasses are force circulated through the housing or a part thereof are known. The increase in volume of the gas in the gas system incident to the evaporation of moisture from the material being dried is typically removed by pre-set vents in the conduit or duct by which the gas is returned from the material exit end fo the material feed end of the dryer. One of the principal disadvantages of these dryers is loss of efficiency because of the lack of control of the amount of gas exhausted through the vents in the gas return conduit as conditions in the drying chamber or section of the dryer varies. Supplemental gas chambers have been employed at the material exit ends of drying chambers to withdraw gas from the material exit ends thereof and prevent the entrance of air at ambient temperature into the dryer chamber through the material exit openings in the dryer. The dryer and method of operation of the present invention provides greater efficiency than prior art dryers by withdrawing the increased gas in the gas system resulting from the evaporation of moisture from the material being dried, and products of combustion when applicable, at the lowest temperature point in the drying process.
Roll conveyors are typically employed in dryers of the type with which the present invention is particularly concerned. Single roll conveyors are usually employed in so-called "board" dryers used in the manufacture of such products as fiberboard, plasterboard, and the like, and double or pinch roll conveyors are typically employed in so-called "veneer" dryers because veneer tends to warp upon drying.